Labour has unearthed a video of Prime Minister John Key on the campaign trail in 2008 ruling out a rise in GST if he won the election.

The video surfaced after Mr Key signalled in his speech to Parliament yesterday that the Government is likely to raise GST to 15 percent from 12.5 percent.

In the video, taken during a press conference in 2008, Mr Key was asked to rule out a hike in GST after suggestions the next government would have no choice but to raise GST to 15 per cent, and raise taxes.

Mr Key's response to the question was: "National is not going to be raising GST. National wants to cut taxes not raise taxes. We acknowledge the point [made], which is that there is a decade of deficits facing New Zealand. But that comes back to our core point ...the fastest way to eliminate those deficits and get New Zealand back into surplus is to get New Zealand growing again."

Mr Key went on to say that if a National government was doing "a half decent job" it wouldn't need to either raise GST or raise taxes.

Asked this morning about the 2008 statement, a spokesman for Mr Key said he had no comment.

Labour leader Phil Goff said Mr Key had broken his promise.

"I think the video speaks for itself. Before the election he promised not to raise GST. Yesterday, he said he will. He's broken his promise, it's a simple as that."